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Abstract:

A thermoplastic polyolefin alloy having high (notched) Izod impact
strength and process for its preparation are disclosed. The alloys of
this invention comprises of a polypropylene block copolymer as a base
polymer, an elastomer, a compatibilizer and optionally a natural filler
and is prepared by melt blending a twin-screw extruder (or
Buss-co-kneader) the above ingredients. The polyolefin alloys of this
invention exhibit very high (notched) Izod impact strength of 60 to 90
kg. cm/cm, flexural modulus of 6,000 to 8,000 kg/cm2, tensile strength at
yield of 150 to 200 kg/cm2, and heat deflection temperature of 60 to
70° C. with 4.6 kgf stress. The alloys also possess melt flow
index of 2-5 g/10 min. when tested according to ASTM D1238 and allow
injection molding, compression molding, thermoforming and other
conventional techniques to be applied for making end products that demand
high impact strength.

Claims:

1. A thermoplastic polyolefin alloy having high (notched) Izod impact
strength comprising a polypropylene block copolymer as a base polymer, an
elastomer and a compatibilizer.

5. Polyolefin alloy as claimed in claim 1, wherein said compatibilizer is
selected from a group of two different ionomers,
styrene-ethylene/butylene-styrene block copolymer (SEBS),
styrene-acrylonitrile copolymer (SAN) and polypropylene block copolymer
grafted with maleic anhydride (PPBC-g-MAH).

6. Polyolefin alloy as claimed in claim 1, wherein said polypropylene
block copolymer is present in an amount of 50 to 95 wt % of said alloy.

7. Polyolefin alloy as claimed in claim 1, wherein said elastomer is
present in a concentration range of 5 to 50 wt %.

8. Polyolefin alloy as claimed in claim 1, wherein said compatibilizer is
present in an amount of from 5 to 30 wt %.

9. Polyolefin alloy as claimed in claim 1, further including a natural
filler.

10. Polyolefin alloy as claimed in claim 9 wherein said filler is selected
from the group consisting of mica, talc and calcium carbonate.

11. Polyolefin alloy as claimed in claim 9, wherein said filler is present
in the concentration range of from 0-10 wt %.

12. A thermoplastic polyolefin alloy having high (notched) Izod impact
strength comprising a base polymer selected from a block copolymer of
propylene and ethylene (PPBC) in the concentration range of 50 to 59 wt
%; an elastomer comprising, a terpolymer made from ethylene propylene
diene monomer (EPDM)/an ethylene propylene copolymer rubber (EPR) in the
concentration range of 5-50 wt %; a compatibilizer selected from the
group consisting of two different ionmers,
styrene-ethylene/butylenes-styrene block copolymer (SEBS),
styrene-acrylonitrile copolymer (SAN) and polypropylene block copolymer
grafted with maleic anhydride (PPBC-g-MAH) in a concentration range of 5
to 30 wt % and natural filler selected from a group consisting of mica,
talc and calcium carbonate in the concentration range of 0 to 10 wt %.

13. Polyolefin alloy as claimed in claim 12, when heated in differential,
scanning calorimeter at a uniform heating rate of 110.degree. C./min. in
nitrogen environment, exhibit 2 to 3 endothermic peaks in the range:
90-167.degree. C.

14. Polyolefin alloy as claimed in claim 12, having exothermic major peak
in the temperature range of 115-25.degree. C. followed by a minor peak in
the range of 113 to 125.degree. C. with total ΔH value in the
range: 55 of 75 J/g, when heated in differential scanning calorimeter at
a uniform heating rate of 10.degree. C./min, in nitrogen environment, up
to 200.degree. C. and cooled after holding isothermally for 3 min.

15. Polyolefin alloy as claimed in claim 12, having melt flow indices in
the range: 2-5 g/10 min. when tested according to ASTM D1238 standard
method using dried granules.

16. Polyolefin alloy as claimed in claim 12, having tensile strength in
the range of 150 to 200 kg/cm2 when tested according to ASTM D638,
using injection molded test specimens.

17. Polyolefin alloy as claimed in claim 12, exhibiting tensile modulus in
the range of 7,000 to 8,000 kg/cm2, when tested according to ASTM
D638, using injection molded test specimens.

18. Polyolefin alloy as claimed in claim 12, exhibiting flexural strength
in the range of 160 to 200 kg/cm2, when tested according to ASTM
D790, using injection molded specimens.

19. Polyolefin alloy as claimed in claim 12, having flexural modules in
the range of 6,000 to 8,000 kg/cm2, when tested according to ASTM
D790, using injection molded specimens.

20. Polyolefin alloy as claimed in claim 12, having heat deflection
temperature in the range of 60-70.degree. C. with 4.6 lcgf stress when
tested according to ASTM D648, using injection molded test specimens.

22. A process for the preparation of a thermoplastic polyolefin alloy
having high (notched) Izod impact strength which comprises melt blending
a polypropylene block copolymer, a terpolymer and a compatibilizer, with
or without a natural filler.

23. A process as claimed in claim 22, wherein said melt blending is
carried out in in a twin screw extruder or a Buss-co-kneader.

24. A process as claimed in claim 22, wherein said polypropylene block
copolymer is a block copolymer of propylene and ethylene.

25. A process as claimed in claim 22, wherein said elastomer is selected
from a terpolymer made from ethylene propylene diene monomer (EPDM)/an
ethylene propylene copolymer rubber (EPR).

26. A process as claimed in claim 22, wherein said compatibilizer is
selected from a group of two different ionomers,
styrene-ethylene/butylene-styrene block copolymer(SEBS),
styrene-acrylonitrile copolymer (SAN) and polypropylene block copolymer
grafted with maleic anhydride (PPBC-g-MAH).

27. A process as claimed in claim 22, wherein said polypropylene block
copolymer is present in an amount of 50 to 95 wt % of said alloy.

28. A process as claimed in claim 22, wherein said elastomer is present in
a concentration range of 5 to 50 wt %.

29. A process as claimed in claim 22, wherein said compatibilizer is
present in an amount of from 5 to 30 wt %.

30. A process as claimed in claim 22, further including a natural filler.

31. A process as claimed in claims 30, wherein said filler is selected
from the group consisting of mica, talc and calcium carbonate.

32. A process as claimed in claim 31, wherein said filler is present in
the concentration range of from 0-10 wt %.

33. A process as claimed in claim 23 wherein said extruder temperature is
maintain at in the range of 125 to 240.degree. C.

34. A process as claimed in claim 23 wherein the
twin-screwextruder/Buss-co-lsneader is operated with the screws rotating
at a speed of 50-100 rpm.

35. A process as claimed in claim 22 wherein the melt blending is carried
out at a residence time of 0.5 to 5.0 min.

36. An article of manufacture whenever made of the polyoelfin alloy as
claimed claim 1.

Description:

FIELD OF INVENTION

[0001]The present invention relates to improved thermoplastic polyolefin
alloys. In particular, the present invention relates to compatibilized
polypropylene copolymer blends prepared by melt blending in a co-rotating
twin-screw extruder (or Buss-co kneader). The compatibilized blends of
this invention exhibit very high notched Izod impact strength at moderate
concentration of elastomer and a suitable compatibilizer along
with/without a natural filler. The present invention also relates to
process for preparing improved thermoplastic polyolefin alloys.

BACKGROUND OF THE INVENTION

[0002]Polymer blends have gained significant commercial growth in the last
2-3 decades outpacing the growth rate of existing polymers by at least
2-5%. Commercial polymer blends are either designed or selected to have
some degree of compatibility between the components to resist
delamination and loss in ductility. Compatibility is to be viewed here as
the ability for the polymer components to co-exist either as molecularly
miscible or morphologically distinct phases but interfacially stabilized
blends, without a tendency for delamination.

[0003]Compatibilization of highly immiscible commercial polymer pairs has
thus far been a technically more challenging task for the polymer blends
technologists in the industry. Significant progress has, however, been
made in recent years in utilizing compatibilizers based on graft or block
copolymer or other interfacial agents that effectively reduce the
interfacial tension between the components to achieve useful levels of
ductility and delamination resistance, while at the same time stabilizing
the morphology against processing effects. Interfacial compatibilization
in commercial polymer blends is generally achieved through reactive
extrusion in which the block or graft copolymer compatibilizer is
generated in situ at the interface during the melt blending.

[0004]Many commercial polymer blends often include an elastomer to improve
the impact strength of the blends under conditions of stress
concentration. The elastomeric dispersions are judiciously employed
within the matrix phase or in the dispersed polymer phase or in both the
phases, depending upon the requirement and the fracture behavior of the
blend. An overwhelming factor in determining the impact strength of an
immiscible or partially miscible blend is the degree and efficiency of
interfacial compatibilization that either is inherent in or has been
designed into the blend system. If the interfacial adhesion or
compatibilization is poor, the elastomer dispersion alone will not
improve the toughness. Combining a high level of (notched) Izod impact
strength with moderate stiffness has been the primary thrust of this
invention.

[0006]In all the above patents, impact resistance was given paramount
importance. Need for high impact materials has been growing as their
applications in several gadgets is ever growing with more and more
industrialization and development of new and innovative machines etc. The
present invention is carried out to fulfill the requirement for a
cost-effective polyolefins blends with very high impact strength with
adequate stiffness and heat deflection temperature. The blends disclosed
in this invention can be used in several applications, such as molded
luggage, furniture, body panels and automotive components, to name a few.

OBJECTS OF THE INVENTION

[0007]It is an object of the present invention to provide compatibilized
blends of polypropylene block copolymer with EPDM or EPR and enhance
miscibility by using a suitable compatibilizer.

[0008]It is another object of the present invention to provide
compatibilized polyolefin blends or alloys using a twin-screw extruder or
a Buss-co-kneader.

[0009]It is yet another object of the present invention to provide an
alloy, with polypropylene copolymer, EPDM or EPR along with a suitable
compatibilizer and other additives that exhibits very high (notched) Izod
impact strength i.e., 60-90 kg. cm/cm, flexural moduls: 6,000-8,000
kg./cm2, heat deflection temperature: 60-70° C., that would
allow injection molding, compression molding, thermoforming and other
conventional techniques to be applied for making end products.

[0010]It still another object of the present invention to provide a
process for preparing a cost effective polyolefin alloy that is suitable
for making end products exhibiting very high (notched) Izod impact
strength along with moderate flexural modulus.

SUMMARY OF THE INVENTION

[0011]The present invention relates to a process for the preparation of
polypropylene copolymer alloys with EPDM or EPR along with a suitable
compatibilizer and with or without a filler, melt-blended in a
co-rotating twin-screw extruder or a Buss-co-kneader all together or in
separate batches, keeping the extruder temperature in the range of
125-240° C. and the screw rotation speed in the range of 50-100
rpm.

[0012]In one embodiment of the invention, the polypropylene copolymer has
a melt flow index in the range of 1-4 g/10 min. when tested at
230° C./2.16 kg. Load (according to ASTM D 1238); and EPDM with
ethylene content in the range of 55-65 wt % possessing specific gravity:
0.86-090, and Mooney viscosity in the range of 36-77 [ML (1+4)
125° C.]; or EPR.

[0013]In one embodiment of the invention, the alloys consist of
polypropylene copolymer as a dominant phase in the concentration range of
50-95 wt %.

[0014]In another embodiment of the invention, the alloy consists of a
compatibilizer picked up from a group of two ionomers,
styrene-ethylene/butylenes-styrene block copolymer (SEBS),
styrene-acrylonitrile copolymer (SAN) and polypropylene copolymer grafted
with maleic anhydride (PPBC-g-MAH) in the concentration I the range of
5-30 wt %.

[0015]In another embodiment of the invention, the alloys also consist of a
natural filler, selected from the group consisting of calcium carbonate,
talc and mica, of a preferred particle size in the range of 10-30 microns
and with a suitable adhesion promoting surface treatment, in the
concentration in range of 0-10 wt %.

[0016]In another embodiment of the invention, the alloys exhibit melt flow
rate in the range of 2-5 g/10 min. when tested according to ASTM D 1238.

[0017]In a further embodiment of the invention, the alloys exhibit an Izod
impact strength (notched specimen) in the range of 60-90 kg. cm/cm., when
tested using injection molded 3.2 mm thick specimens (cut from the mid
portions of the tensile bar of Type-I described in ASTM D638), and 50-70
kg. cm/cm when tested using 6.4 mm thick specimens, according to ASTM D
256.

[0018]In yet another embodiment of the invention, the alloys exhibit
flexural modulus in the range of 6,000/8,000 kg/cm2, when tested
according to ASTM D 790.

[0019]In another embodiment of the invention, the alloys exhibit tensile
strength in the range of 150-200 kg/cm2, when tested according to
ASTM D638, using injection molded specimens.

[0020]In another embodiment of the invention, the alloys show heat
deflection temperature in the range of 60-70° C. with 4.6 kg the
present invention to provide stress and 45-55° C. with 18.2 kgf
stress according to ASTM D648.

DETAILED DESCRIPTION OF THE INVENTION

[0021]A polyolefin polymer, viz., propylene ethylene block copolymer
(PPBC) was the preferred matrix material for carrying out the present
invention. It was obtained in the form of granules after adequately
adding the stabilizers and antioxidants soon after polymerization. The
granules were dried at 80±5° C. for two hours, preferably, in
an oven with air circulation facility. An elastomer, ethylene propylene
copoylmer rubber (EPR) or ethylene-propylene-diene monomer (EPDM), in a
preferred form of granules, was also dried separately in an air
circulating oven at a preferred temperature of 80±5° C. for a
period of two hours. A compatibilizer selected from a group of two
ionomers, styrene-ethylene/butylenes-styrene block copolymer (SEBS),
styrene-acrylonitrile copolymer (SAN) and polypropylene copolymer grafted
with maleic anhydride (PPBC-g MAH) was also dried at the same above
temperature for the same time. Similarly, a natural filler, picked up
among a group of mica, talc and calcium carbonate, preferably with a
particle size in the range of 10-30 microns, was also dried at the same
temperature, mentioned above, for the same time.

[0022]The object of melt blending, by means of a twin-screw extruder or
Buss-co-kneader with a specially designed screw profile, is to break the
elastomer into as fine particles as possible and to disperse them
uniformly within the matrix of polypropylene block copolymer. This
intimate associated with the presence of a suitable compatibilzer would
yield an alloy that would exhibit desired mechanical properties,
especially enhanced impact strength.

[0023]Dried PPBC, elastomer, compatibilizer, with or without a filler,
along with other ingredients were tumble--mixed in the composition given
here: PPBC: 50-59 wt %, EPR/EPDM: 5-50 wt %, compatibilizer (s) 5-30 wt
%, filler: 0-10 wt % initiator, sulfur and other additives viz., glycerin
mon-stearate, Tinuvin-770, Tinuvin-327, B-blend-225 and Chimmasorb, a
combination of Tinuvin-622 and Benzophenone 0.01-0-10 phr each. This
tumble-mixed dry mixture was extruded in a co-rotating twin-screw
extruder (or a Buss-co-kneader) with a preferred screw profile under the
following conditions: temperature range: 125-240° C., screw speed:
50-100 rpm, residence time: 0.5-5.0 min. The extrudate was dipped in cold
circulating water and was chopped into granules of length 34 mm.

[0024]The extrudated granules were dried and then injection molded into
ASTM standard test specimens for evaluating various performance
properties such as tensile strength, flexural modulus, notched Izod
impact strength and heat deflection temperature. Injection molding was
carried out using a computer-controlled injection molding machine having
four heating zones operating in the range: 130-230° C., injection
pressure (applied in six stages) 60-100 kg/cm2, injection time (in
six stages) 2-6 sec. With screw speed (in two stages) in the range:
90-105 rpm. The standard test specimens, thus obtained were used for
testing various mechanical properties of the alloys (mentioned above)
following the ASTM standard test methods.

[0025]Other tests, such as melt flow index, crystallization kinetics
(using Differential Scanning Calorimeter) and filler content (using
Thermogravimetric Analyzer) were carried out using dry granules of the
alloys. Dispersions of the elastomer and the filler were studied using
thin microtomed sections cut from the injection molded flexural bars,
using polarized optical microscope.

[0026]Rubber toughening is the most often used method of improving the
impact resistance of polymers. In impact-modified materials, the
composition of the constituents, their miscibility and the morphology
influence the deformation and failure mechanisms in the blend. Particle
size of the elastomer, its dispersion and its adhesion, (if required by
the use of a suitable compatibilizer), with the matrix are also the
important factors determining the toughness of the blend.

[0027]In the case of PPBC blends with EPDM/EPR, the elastomer was found to
reduce the crystallinity of PPBC and significantly influence its failure
mechanism. Both crazing and shear yielding, responsible mechanisms for
plastic deformation in rigid polymers, found to be operating
simultaneously in these blends. These two mechanisms are not mutually
exclusive, but under certain conditions both operate simultaneously. They
were found to be responsible for toughening the matrix materials, PPBC.

[0028]The present invention will now be described in greater detail by the
following examples, the purpose of which is merely to illustrate the
invention and not limit the scope thereof.

EXAMPLE-1

[0029]Dried Granules of polypropylene copolymer 60 wt % were mixed with
dried EPDM of concentration 20 wt %, a dried preferred compatibilizer,
styrene-acrylonitrile copolymer (SAN) 5 wt %; PPBC grafted with maleic
anhydride (PPBC-g-MAH) 5 wt % and a natural filler, preferably talc, 10
wt %, and all the constituents were tumble-mixed thoroughly. The dry
mixture was extruded in a twin-screw extruder (or a Buss-co-kneader) with
co-rotating screws, having a preferred screw profile with an objective of
intimate mixing of the ingredients. The extruder was operated in the
temperature range: 125-240° C. with screws rotating at a speed:
50-100 rpm. The extrudate strand (referred to as Alloy-A) was dipped in a
trough of circulating cold water. The strand was later dried and
granulated.

[0031]The performance properties of the alloys, injection molded under the
above conditions, are given below in Table-II. For each property reported
here, at least six specimens were tested and the average value was
calculated.

[0032]Moisture free granules of polypropylene copolymer 72 wt % were mixed
with dried elastomer preferably, EPR of concentration 23 wt % and a dried
compatibilizer, preferably, styrene-ethylene/butylenes-styrene block
copolymer (SEBS) 5 wt %. All the constituents were thoroughly tumble
mixed and then extruded in the same extruder under the same conditions
mentioned above in Example-1. The extrude (referred to as Alloy B) was
granulated and standard ASTM test specimens were prepared using the same
injection molding machine under the same conditions mentioned in the
above example. The properties Alloy-B are presented in Table-III.

[0033]Polypropylene copolymer, 45 wt %, polypropylene copolymer grafted
with maleic anhydride (PPCP-g-MAH), 45 wt %, and an elastomer; preferably
EPDM, 10 wt %, were all weighed and dried. All the constituents were
mixed thoroughly and then extruded in the same above-mentioned extruder
under the same extruding conditions. The extrudate (referred to as
Alloy-C) was granulated and standard ASTM test specimens were injection
molded as mentioned in the previous examples. The properties of Alloy-C
are given in Table-IV.